Mobile devices may incorporate multiple antennas, or an antenna array, for diversity reception and for implementing spatial multiplexing. Spatial multiplexing involves splitting a high data rate signal into two or more separate data streams that are intended to arrive at a receiver antenna array with different spatial signatures such that the two or more separate data streams can be reassembled to construct the high data rate signal. At least two separate mobile device antennas, or two antenna elements of an antenna array, each receive one of the separate data streams. Therefore, spatial multiplexing may be considered a form of antenna diversity reception.
The goal of antenna diversity reception is to take advantage of decorrelation between the diversity antennas. The decorrelation may be achieved by physical placement, polarization or by using differing antenna beam patterns. Mobile device diversity and MIMO (multiple-input, multiple-output) antenna systems have been developed based on static figure-of-merit (“FoM”) requirements, total efficiency, gain imbalance and envelope correlation coefficient values (i.e. antenna correlation) that are fixed regardless of prevalent operating parameters or the environment in which the mobile device is operating.
Performance of the MIMO system may be negatively impacted by changes in the radiated channel conditions and the user's position and handgrip on the mobile device, because the hand position may impair radio frequency (RF) reception by the MIMO antennas. For this and other reasons, challenges exist for achieving good performance of diversity antenna systems in a mobile device.